There are a number of lens designs presently in existence which have design regimes which enable achievement of various effects relating to interplay between the cornea, the lens and the eye lids of a wearer, especially in assisting with lens orientation on the eye of a wearer.
In the past, lenses (which usually have a circular appearance from a plan view and a concave outward appearance from a side view) have had machining performed on them in various ways in an attempt to provide a lens configuration which will enable correct lens orientation on the eye as well as adequate control of the lens on the eye of the wearer. Traditionally, the correct lens orientation on the eye has been achieved by providing on the lens surface, machined prisms, wedges and truncations.
In implementation of these designs it is also necessary for the designer to consider the requirement of transmission of gas between the lens and the cornea. Low gas transmission may create problems on the eye of a wearer which stem from not allowing the eye to breathe.
A contact lens sits in apposition with the cornea or the sclera or both. It is important that a lens be able to transmit or allow a passage of oxygen to reach the eye so that natural conditions can be maintained as far as is practical near the eye and on the eye surface. Proper orientation of a lens on the eye is necessary for proper correction of astigmatism.
When a lens is oriented in the proper direction, the astigmatic error in the lens is closely coincidental with the astigmatic error in the eye. It is essential that this be achieved to prevent visual acuity deteriorating.
The prior art lenses achieve orientation by three main ways. The first relates to prism formation on the lens. This is achieved by machining of the lens surface to allow the eye lids to complement the lens surface configuration thereby assisting in proper location of the lens. In one configuration the lens is thickened towards the bottom.
The second method of lens orientation is achieved by zonal thinning. In this case, the top and bottom peripheral areas of the lens are thinned by machining. The eye lid pressure then moves the lens around to find the line of least resistance to thereby hold the lens in the correctly oriented position. The former method of lens orientation suffers from a number of disadvantages namely the aforesaid thickened portion of the lens may prevent adequate oxygen transmission through the lens. This can result in oedema or corneal neovascularisation. Another consequence of the lens thickening is wearer discomfort.
The zonal thinning method also has disadvantages. Namely, using this method it is difficult to make a lens to the required degree of accuracy and reproduceability. The degree of orientation accuracy is not always as good as required and zonal thinning does not work well for high positive corrections due to the thinness of the periphery of the lens. The third method of lens orientation which was provided for a lens was to have grooves and/or patterns forming grooves in the front or back surfaces of the lens. The grooves and/or patterns aid in the correct orientation of the lens on the eye and increase gas transmission through the lens.
Preferably in lenses designed in this way there are a series of grooves or patterns on the lens which are held by the upper eye lid thus aiding lens orientation. When these lenses are inserted on the eye, during the blink action, the spungy palpabral and/or tarsal burbar conjunctiva grips the indentation in the lens surface and orientates the lens by following the slope of the pattern or grooves.
The grooves and/or patterns formed on the lens facilitate proper orientation on the eye and without compromise to the relationship between the cornea, conjunctiva and lens thereby eliminating discomfort and eye irritation from the contact lens.
This known type of lens configuration has many advantages over the earlier designs, for instance, no increase in the lens thickness nor chamferings of the lens surface is necessary for lens orientation. These grooves or patterns can be applied to bifocal contact lenses to improve location of the lens for alternating vision.
Although the overall concept of utilising patterns and grooves is known, that concept has to date been in its early experimental stages such that it has hitherto previously been unclear as to exactly how the lens is oriented on the eye according to the particular force regime generated by a pre-selected groove or pattern configuration. The grooves and/or patterns can be formed on either the back or front surface of the lens according to requirements.
The patterns and/or grooves known in the prior art methodology provide a means for harnessing lid forces and various physiological forces pertaining specifically to the eye and its various movements and actions. To date, apart from experimentation with the pattern and groove concept, it has not previously been disclosed as to exactly how using those patterns and grooves the lens properly orientates on the eye of a wearer.
After considerable experimentation it has been found that there is an optimum lens surface relief design for enabling proper orientation on the eye. Furthermore, it can now be indicated exactly how the forces transmit on and about the optimum lens surface relief design to enable proper orientation on the eye of a wearer.